The invention essentially relates to a spiral stent forming device as well as to a method of making it.
It is known that devices forming endoprotheses, also known as xe2x80x9cstentsxe2x80x9d, enable treating narrowing of various canals of the human anatomy, such as an artery, and to keep them open.
Several types of stents exist: tubular, network, filamentary, balloon-expandable or self-expandable stents.
For example, the document U.S. Pat. No. 5,578,149 as well as U.S. Pat. No. 5,591,230 describe a stent which is formed by a filamentary element coiled in a spiral and having bends which define a zigzag structure, enabling a significant radial expansion with a low shortening of the length of the stent.
The fault of these stents is that they have a weak shoring up strength at the ends and poor covering power at the ends.
Furthermore, it is also known from U.S. Pat. No. 4,553,545, of various embodiments of a stent which is formed by a filamentary element coiled in a spiral. With reference to FIG. 10 of this patent, a risk is presented of shifting or of crushing or of unwinding of the stent during a radial expansion, and this is also explained in column 7, lines 56 et seq. In order to remedy this, this patent proposes rigidifying the turns by a rigidifying element, see FIGS. 11 to 16. A stent of ladder construction is then proposed in FIGS. 22 and 23, and notably with reference to FIG. 23, a stent is formed by a double helix spiral which is joined by transversal elements 82. It is indicated that this structure enables improving the stability during a radial expansion (column 12, lines 45 to 66).
The fault of these stents is that they have a weak shoring up strength at the ends and poor covering power at the ends.
Further, if an obstacle is encountered during the insertion of the stent forming device, due to the absence of hold of the spiral at the ends, a subsidence of the spiral can be produced in some cases.
It is further known from the document WO-A-96/03092, of a stent forming device which is constituted by a filamentary element coiled in a ring-like fashion, which is constituted of a certain number of rings joined together by bent binding elements 22, the ring-like portions being also bent so as to form a zigzag structure. This device has a good shoring up strength during a radial expansion. This device has a certain flexibility by virtue of the presence of joints 22 comprising bends 20, between the ring-like elements 11, but this flexibility is essentially lost after expansion and gives rise to constraints on the canals, and in particular the arteries. It will be observed that the structure described in this document provides, after unfolding, a network or cellular system, as is clearly represented in FIG. 4, which favors the shoring up, but limits the flexibility and the shapability to the canal, and this constitutes a significant requirement.
The current limits of these known stent forming devices remain:
a) the rigidity of certain stents, which can compromise an access to certain lesions, the upstream of which is winding. This rigidity becomes a drawback insofar as stent forming devices of longer length are more and more sought after, at the same time as the stent forming devices being capable of making winding accesses and for which a greater flexibility is sought. The stent forming device described in the document WO-A-96/03092 has a flexibility which is improved with respect to the prior art devices, but which is still judged to be insufficient, notably in the case of long lengths, i.e. beyond 20 mm, which is the current tendency.
b) the constraints given rise to on the artery upstream and downstream from the stent resulting from a drawing out phenomenon by rigidification of the canal after unfolding of the stent. This can give rise to complications during the intervention of tissue reactions leading to a recurrent narrowing of the canal mentioned above. This leads to an insufficient shapability to the canal, and notably to the ends, giving rise to constraints which are not very satisfactory to said ends, and this in particular is the case in the document WO-A-96/03092.
c) the difficulty of getting over the stent when it is implanted straddling over a bifurcation and that the branch must be treated as well. In particular, it may be necessary to pass a balloon or a stent on balloon through the structure of the first stent. This also is in particular the case in the document WO-A-96/03092.
d) Certain stents lack radial strength, called shoring up strength, in particular at the ends, and this can be important for shoring up the origin (ostium) of a canal such as an artery, which is in general very elastic. This is in particular the case of stent forming devices described in the documents U.S. Pat. No. 5,578,149, U.S. Pat. No. 5,591,230, and U.S. Pat. No. 4,553,545. The shoring up strength of the whole of the stent is also very important when lesions exert a strong resistance to the dilatation, as is the case of calcified lesions or lesions having strong elastic recoil.
e) Certain filamentary type stents deform longitudinally during a blockage of the progression during the access to a lesion due to a lack of hold of the structure. This is in particular the case of the stent forming devices described in the documents U.S. Pat. No. 5,578,149, U.S. Pat. No. 5,591,230, and U.S. Pat. No. 4,553,545.
Thus, in the known prior art devices, these are of a design which is either entirely spiral, or entirely ring-like. Further, for certain ring-like type stents, these can be produced in a network, as in the case of the document WO 96/03092.
Thus, the main aim of the present invention is to solve the novel technical problem consisting of providing a solution, which consists of a novel stent forming device, which has simultaneously the following properties:
a) a very good flexibility,
b) a lateral crossing capacity from the inside of the stent by another stent or a balloon device,
c) a very good shapability in the longitudinal sense, so as not to modify the curvature of the canal in which the stent must be implanted, in the longitudinal sense,
d) a very good radial strength so as to completely fill its role of shoring up the canal in which the stent must be implanted,
e) a very good crossing capacity enabling a longitudinal passage by another device such as a balloon or another stent, optionally also on a balloon,
f) a very good capacity to keep in place in unfolded position,
g) a very good capacity of shoring up and of ring-like covering of the ends enabling a complete covering without overrunning, which is particularly important notably in the medical field at the level of ostia.
h) an expansion essentially without shortening of the length of the stent, and this even for stents of long lengths, namely greater than about 20 mm.
Thus, a further main aim of the invention is to provide a solution to the novel technical problem above, according to a particularly simple design which is relatively inexpensive and which can be used on an industrial and medical scale.
Thus, according to a first aspect, the present invention provides a stent forming device comprising a first filamentary element coiled spirally at least in its central portion, and a proximal end portion and a distal end portion, characterized in that it comprises a second filamentary element coiled spirally at least in its central portion, said first and second elements thus defining a double helix structure, and in that at least one, preferably both, end portion(s) is (are) produced with at least one said filamentary element coiled in substantially ring-like fashion. This device enables thus reinforcing notably the maintenance of the structure in place as well as ensuring a complete covering without running over, particularly at the level of the ostium.
According to an advantageous embodiment of the invention, the device comprises end portions defining respectively a proximal end edge and a distal end edge of the device, said end portions being produced with said first and second filamentary elements coiled in substantially ring-like fashion and joined onto said central portion composed of the first element and of the second filamentary element mentioned above in a double helix.
According to another advantageous embodiment of the invention, said first element and said second filamentary elements forming a double helix structure mentioned above are bent so as to produce a zigzag form, in producing here a spiral zigzag form.
According to a variant enabling a good transversal crossing, the central portion in a double helix comprises at least 3 bends defining at least 3 vertices per 360xc2x0 turn.
According to a particular embodiment of the invention, the end portions produce a general ring-like form which is joined directly or via at least one joint to the central portion in a double helix.
According to another particular embodiment of the invention, the proximal edge and the distal edge of the ends are comprised in a plane of circular cross-section, the center of which substantially coincides with the longitudinal axis which is defined by at least the central portion mentioned above in a double helix.
According to an advantageous variant, the proximal edge and the distal edge are comprised in a plane of circular cross-section which is substantially perpendicular to the longitudinal axis which is defined by at least the central portion mentioned above in a double helix.
According to another variant of the invention, the proximal edge and the distal edge are comprised in a plane of circular cross-section forming an acute angle with the longitudinal axis of the device, of between less than 90xc2x0 and at least 60xc2x0, preferably between less than 90xc2x0 and at least 70xc2x0.
According to another advantageous embodiment of the invention, said first filamentary element and second filamentary element are joined together by at least some linking arms spaced out along said central portion.
According to a variant, the double helix being composed of successive 360xc2x0 turns, at least some turns comprise at least one linking arm between the first element and the second element. Advantageously, each 360xc2x0 turn comprises at least one linking arm.
According to another variant, each turn comprises at least two linking arms.
According to yet another particularly advantageous variant, some linking arms or each linking arm can be itself bent in having one or more bends so as to improve the flexibility enabling also improving the ability to be shaped to the canal.
According to yet another advantageous embodiment of the invention, the linking arms mentioned above produce a size which is sufficient to enable a sufficient space to be defined between the first and the second spiral elements mentioned above, for the passage of a tool in an adjacent canal to the canal in which the stent forming device has been disposed.
Advantageously, the length of the linking arm is of the order of at least 0.5 mm. Advantageously, the length of the linking arm will be of between about 0.5 mm and 5 mm.
According to yet another variant, the central portion comprises at least one reinforcing joint r joining in two vertices CO of two successive spiral turns. Advantageously, these reinforcing joints r can be of a number of one or more per turn, advantageously in a staggered manner with respect to the linking arms.
According to another embodiment of the invention, the straight cross-section of at least one or both said first and second filamentary elements mentioned above is selected from the group consisting of a straight circular section, of a straight polygonal cross-section such as square, rectangular, pentagonal, hexagonal or octagonal, of a straight polygonal cross-section having rounded edges, such as square having rounded edges or rectangular having rounded edges, or of a straight oval cross-section.
According to a particular embodiment, the size of the straight cross-section is related directly to the size of the straight cross-section of the canal in which the stent forming device must be inserted. Furthermore, generally, the diameter of said first element or of said second element, or of both, is of between about one hundredth and about one tenth of the diameter of the straight cross-section defined by the ring-like end portion of the stent forming device, in its initial ready-to-use machining form.
Advantageously, the diameter of the linking arm will be substantially equal to the diameter of said filamentary element, advantageously the shape of the linking arm is also substantially identical to that of the filamentary element.
According to an embodiment, said first filamentary element or the second filamentary element, or both, define a spiral having an inclination with respect to the longitudinal axis, at least in the central portion mentioned above, of between about 45xc2x0 and about 80xc2x0, advantageously of between about 50xc2x0 and 70xc2x0, and currently preferably of about 60xc2x0.
According to yet another embodiment of the invention, each bend of the filamentary element mentioned above has an acute angle which is defined by two successive portions of the filamentary element, of between about 20xc2x0 and about 60xc2x0.
According to another advantageous embodiment of the invention, the stent forming device mentioned above is made as a monoblock, without soldering, from its proximal end to its distal end, and this simplifies its preparation and removes any risk of corrosion and rupture.
Within the context of the invention, any material which is compatible with an implantation into the body of a mammal, preferably man or an animal, can be used as material constituting the stent forming device. Such materials are generally constituted of a biocompatible material, particularly a biodegradable polymer or a metal such as a stainless steel of medical quality, a material having of shape memory, for example a material based on an alloy of nickel and titanium. Materials of low elastic memory can be used which can undergo an irreversible plastic deformation in exerting a radial mechanical force from the inside out towards the exterior, as is well-known to the person skilled in the art.
According to a second aspect, the present invention also provides a method of making the stent forming device mentioned above, characterized in that it comprises cutting out a tubular element of full cylindrical surface in a way so as to define in this tubular element said central portion in a double helix, as well as the end portions mentioned above. Thus, it is possible to make the stent forming device as a monobloc and without soldering from one end to the other.
According to an advantageous embodiment, this cut-out is produced so as to define the precise embodiment sought in its initial form to be used as such.
According to a third aspect, the present invention also provides another method of making the stent forming device mentioned above, characterized in that a cut-out is made of a flat element or plate, so as to define the central portion mentioned above, which is intended to form a double helix by coiling on itself around a chuck of suitable shape, preferably having straight circular cross-section, said cut-out also producing the end portions mentioned above. Thus, it is possible to make the stent monoblock, but a soldering at each end is necessary after the coiling.
These cut-outs are produced with the aid of methods and devices which are well-known to the person skilled in the art. The person skilled in the art knows for example of machining techniques by laser, notably of the YAG or CO2 type, or other, by electroerosion, or by a combination of the two; the electroerosion technique is also known as xe2x80x9cetchingxe2x80x9d. It is understood that when one starts off from a tube, the technique by laser ray consists in attacking the external surface of the tube by the laser beam so as to define the structure sought after, such as here the double helix structure in the central portion.
Further, when a thin plate is used, for example a rectangular plate, the laser beam machines in this plate the structure of the invention comprising the double helix in its central portion. Then, it will be sufficient to roll the structure obtained on a cylindrical chuck and finally to solder the edges of each of the ends.
Starting either from the tube, or from the thin plate, it N is also possible to use the technique of electroerosion or xe2x80x9cetchingxe2x80x9d mentioned above.
According to a fourth aspect, the present invention provides another method of making the stent forming device mentioned above, characterized in that a cut-out is made from a flat element or plate, or from a tube, with the aid of a device for projecting a liquid under pressure, in particular water, of the Karcher(copyright) type.
According to a fifth aspect, the present invention also covers a method of preparation according to which said first filamentary element mentioned above of spiral shape and a second element independent filamentary of spiral shape are first of all made, and then said first element and second element are joined, according to a determined pitch, to end portions defining a proximal edge and a distal edge of the type described above within the context of the invention optionally with the presence of linking arms and/or of joints as described above.
By virtue of the invention, the technical problems set forth above are solved in a simple, relatively inexpensive manner which is usable on an industrial and medical scale.
Within the context of the present invention, it is observed that by a combination of essentially ring-like end(s) and spiral type central portion, the simultaneous obtaining of the whole of the requirements set forth above is lead to in an unexpected way for a person skilled in the art, namely, a very good flexibility, a very good capacity to lateral crossing from the inside, a very good shapability in the longitudinal sense, a very good radial strength, in particular at the ends, a very good shoring up capacity and ring-like covering at the ends enabling a complete covering without running over, an expansion which is essentially without shortening of he length of the stent, a very good capacity to crossing enabling a longitudinal passage by another device, such as a balloon, or another stent, optionally also on-balloon, a very good capacity of maintenance in the unfolded position combined with a very good drawing out capacity, even in the spiral central portion, and this even for stent forming devices of long lengths, i.e. of lengths longer than about 20 mm, and for sizes which can be greater than 50 mm.
Further, the invention, by combination of a spiral central portion, preferably a zigzag, with substantially ring-like ends, an easy setting is allowed on a positioning device, notably of the balloon type, and this was not allowed by the prior art devices of the spiral type, such as described in the U.S. Pat. No. 4,553,545.
The invention is further applicable to self-expandable devices or to non-self-expandable devices.
Other aims, characteristics and advantages of the invention will appear clearly in the light of the following explanatory description made with reference to the annexed drawings, which represent several currently preferred embodiments of the invention, which are given simply as an illustration, and which will in no way limit the scope of the invention.